The invention relates to a vacuum circuit breaker with two switching tubes for each pole, which are electrically connected in series and arranged substantially coaxial. The circuit breaker includes an actuating device that is common to both tubes for closing and breaking the circuit. It also includes an offsetting drive mechanism to produce two motions that are contrary to one another with respect to a uniform drive motion, and a contact pressure spring assigned to each switching tube.
A vacuum circuit breaker of this type is described, for example, in the periodical Electrical Review, Apr. 13, 1973, at pages 531 to 533 and in the periodical Elektrische Bahnen 78 (1980), Volume 8, at pages 198 to 202. Further examples of vacuum circuit breakers of this kind are found in Catalogue GB64/1949 for vacuum circuit breaker Model VT-123 manufactured by the Meidensha Co. and in U.S. Pat. No. 3,597,556.
In vacuum circuit breakers with switching tubes that are connected in series and arranged coaxially, the contacts must open and close simultaneously to avoid overloading of one of the two switching tubes due to the breaker current. This can be achieved by adjustment of the coupling elements that are usually provided at the drive tappets of the switching tubes. This process, however, is tedious and very difficult to perform without errors.